1. Field of the Invention
The present invention relates to a technique of reducing the probability of occurrence of a short circuit between power supplies in a display panel having a display area with a matrix array of display elements.
The present invention relates to a display panel, an electronic device, and a method of making the display panel.
2. Description of the Related Art
Recently, flat panel displays (FPDs) have remarkably become widespread. Displays of various types are proposed along with the widespread use of FPDs. In the current FPD field, liquid crystal displays (LCDs) are predominantly used.
LCDs, which are not self-light-emitting devices, need additional components, such as a backlight and a polarizer. Accordingly, the LCDs have disadvantages in that it is difficult to reduce the thickness and the brightness tends to degrade.
In contrast, organic electroluminescent (EL) displays, which are self-light-emitting devices, need no additional components, such as a backlight, in principle. Advantageously, a reduction in thickness and an increase in brightness of the organic EL displays are easier than those of the LCDs.
In particular, active-matrix organic EL displays in which a drive circuit (switching element) is provided for each display pixel have advantages in that low current consumption can be achieved because each display pixel can hold light emission.
The active-matrix organic EL displays further have advantages in that the displays having a large screen and those having a high-definition screen can be relatively easily realized. Accordingly, the active-matrix organic EL displays are expected to enter the mainstream of next-generation FPDs.
FIG. 1 illustrates the structure of a panel of an organic EL display.
The organic EL display, indicated at 1, includes a glass substrate 3 as a base substrate. The upper surface of the glass substrate 3 has a display area 5 with a matrix array of display pixels. The display pixels are driven by active matrix driving.
Scan-signal supply TABs 7, video-signal supply TABS 9, and power supply TCPs 11 are connected to the glass substrate 3 so as to surround the display area 5. The scan-signal supply TABS 7 are used to supply signals for controlling a video-signal write operation and a light emission operation on the display pixels.
The video-signal supply TABs 9 are used to supply video signals for the display pixels. The power supply TCPs 11 are used to supply drive power.
In addition, a cathode layer is arranged on the upper surface of the display area 5 so as to cover the whole of the display area 5 (or an organic-layer deposition area 13). The organic-layer deposition area 13, serving as a range where an organic material for a luminous layer is deposited, is slightly larger than the display area 5.
A cathode-layer deposition area 15, which provides a maximum area for cathode layer formation, is larger than the organic-layer deposition area 13 by approximately 1 to 2 mm in each side. The cathode layer is held at 0 V by a cathode common electrode 17, indicated by a hatched portion in FIG. 1, electrically connected to the cathode layer in the periphery of the cathode-layer deposition area 15.
Those deposited layers are coated with a sealing compound (not shown) and the sealing compound is then overlaid with a sealing glass, thus constructing the organic EL display 1.
FIG. 2 is an enlarged view of related-art arrangement in the vicinity of the power supply TCP in the organic EL display 1. A cathode power supply pad supplies-cathode power to a cathode power supply lead pattern 21.
The cathode power supply lead pattern 21 is connected to the cathode common electrode 17 via a contact 23. The cathode common electrode 17 is frame-shaped so as to be arranged along the periphery of the display area 5 and is electrically connected to the cathode layer deposited in the cathode-layer deposition area 15.
An anode power supply lead pattern 25 is connected to an anode power supply pad. The anode power supply lead pattern 25 is a metallization pattern underlying the cathode common electrode 17 and is connected to the display pixels in the display area.
FIG. 3 illustrates the cross section of part where the cathode common electrode 17 overlaps the anode power supply lead pattern 25. In other words, FIG. 3 is a cross-sectional view taken along the line A-A in FIG. 2.
The anode power supply lead pattern 25 is arranged on the upper surface of the glass substrate 3 and is covered with a protective layer 31.
The protective layer 31 is overlaid with a planarizing layer 33, which is covered with the cathode common electrode 17.
The cathode common electrode 17 is coated with the sealing compound indicated at 35. The sealing compound 35 is covered with the sealing glass indicated at 37. The above-described layered structure is of a general type.
Related-art organic EL displays are disclosed in Japanese Unexamined Patent Application Publication Nos. 2005-164679, 2005-19151, and 2003-100447.